Evaluation of carbon steel corrosion in vicinity of interface sea-water/sea-mud by techniques WBE and LP

Serious corrosion problem could be found in the vicinity of the interface sea-water/sea-mud (VISS) for marine structures of steels. The corrosion of carbon steel in an artificial environment as a simulation of the above VISS was studied by means of wire beam electrode (WBE) technique, linear polarization (LP) technique, electrochemical impedance spectroscopy (EIS) and corrosion morphology examination etc. For the simulated VISS, the sea-water and sea- mud were taken directly from Zhanjiang bay of the South China sea. The galvanic current between one electrode and another electrode among the rest 99 electrodes was successively measured by WBE technique, and the change of the cathode area and anode area was acquired from the results of the measurement of galvanic current. The E_corr and I_corr of the electrodes of carbon steel, which were perpendicular to the interface of sea-water/sea-mud (ISS), were obtained by the linear polarization technique. Then the corrosion morphology of the tested electrodes was observed by stereo microscope. The results show that the portion under ISS of an immersed electrode of carbon steel acts as anode, and that above ISS acts as cathode. The corrosion of carbon steel in the VISS was controlled by the potential difference, the dissolve oxygen concentration and the sea-mud impedance. The areas both of where near by the ISS on the anode portion and where far from the ISS on the cathode portion were the serious corrosion areas. Correspondingly of which the formed corrosion product on the former was fluffy and low adhesive, while that on the later was compact and strongly adhesive.